By Wayne Kirkbride
Modesto Bee
January 13, 2014

TWAIN HARTE – Here in the Sierra where I live, the snowfall we experienced in early December gave us hope that a normal snowpack would mean an end to the below-average precipitation of the prior year. As the snow melted with rising temperatures, it became evident we were in for another dry year. What worries me and the scientists who study climate is the history behind the West’s climate over the centuries.

In a recent report, a phenomenon called the Pacific Decadal Oscillation was suggested as a reason that a high pressure ridge has persisted over the state. Climatologist Bill Patzert, who works for NASA’s Jet Propulsion Laboratory, said droughts in California often are associated with a negative PDO, meaning a cooler northern Pacific Ocean. He says a negative PDO could signal that we are in the midst of a decades-long drought that began in 2000.

A doctoral candidate at Stanford, Daniel Swain, has studied relevant weather records dating to 1948; he believes such a persistent ridge has never been seen before.

Whether one accepts the planet is warming and changing weather patterns are due to man-made causes or believes natural forces are at work, or both, there are at least two more studies that should grab our attention as a wake-up call. One, done by the National Oceanic and Atmospheric Administration, studied tree-ring growth over the past 500 years.

“Longer records show strong evidence for a drought that appears to have been more severe in some of central North America than anything we have experienced in the 20th century, including the 1930s drought,” NOAA wrote.

A study of the bristlecone pine from the White Mountains of eastern California show multi- decadedroughts of the periods around A.D. 929 and 1299

Professor Scott Stine of California State University, East Bay, studied ancient tree stumps at Mono Lake and the Walker River in the Sierra. He found “evidence of medieval droughts of the Sierra that were the most severe of the past 4,000 to 7,000 years (from A.D. 900-1300). Conditions of the past 150 years drew down lakes and rivers well below their modern levels on numerous occasions during the late 18th and 19th centuries.”

Stine goes on: “Indeed, increasing evidence indicates that there is little that is climatically ‘normal’ about the past century and a half; it appears, in fact, to be California’s third or fourth wettest … period of the past four or more millennia. Since statehood, Californians have been living in the best of climatic times. Drier times undoubtedly lie ahead.”

The latest data confirming global warming caused by man do not negate studies that show that climate’s natural variability might be greater than previously known. Science must look back over centuries and even millennia to understand the weather cycle that might be swinging back around in our lifetime and certainly for the future population of the earth.

Maury Roos, of the California Department of Water Resources, said that about 35 percent of the state’s usable water comes from our Sierra snowpack.

That December storm is now just a memory. By Christmas, the weather was clear and 80 degrees in Southern California and low 70s in the north of the state.

The entire state needs to take steps immediately to conserve water. There might be a lot of economic and lifestyle changes ahead for all of us.

Kirkbride lives in Twain Harte and writes about Mother Lode and Sierra matters. Send questions or comments to columns@modbee.com.

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